228
Type Description
location-based applications.
NOTE:
•
If the MAC/PHY configuration/status TLV is not advertisable, none of the LLDP-MED TLVs will be
advertised even if they are advertisable.
•
If the LLDP-MED capabilities TLV is not advertisable, the other LLDP-MED TLVs will not be
advertised even if they are advertisable.
Management address
The network management system uses the management address of a device to identify and manage
the device for topology maintenance and network management. The management address is
encapsulated in the management address TLV.
Working mechanism
LLDP operating modes
An LLDP agent can operate in one of the following modes:
•
TxRx
mode
—An LLDP agent in this mode can send and receive LLDP frames.
•
Tx
mode
—An LLDP agent in this mode can only send LLDP frames.
•
Rx
mode
—An LLDP agent in this mode can only receive LLDP frames.
•
Disable
mode
—An LLDP agent in this mode cannot send or receive LLDP frames.
Each time the LLDP operating mode of an LLDP agent changes, its LLDP protocol state machine
reinitializes. A configurable reinitialization delay prevents frequent initializations caused by frequent
changes to the operating mode. If you configure the reinitialization delay, an LLDP agent must wait
the specified amount of time to initialize LLDP after the LLDP operating mode changes.
Transmitting LLDP frames
An LLDP agent operating in TxRx mode or Tx mode sends LLDP frames to its directly connected
devices both periodically and when the local configuration changes. To prevent LLDP frames from
overwhelming the network during times of frequent changes to local device information, LLDP uses
the token bucket mechanism to rate limit LLDP frames. For more information about the token bucket
mechanism, see
ACL and QoS Configuration Guide
.
LLDP automatically enables the fast LLDP frame transmission mechanism in either of the following
cases:
•
A new neighbor is discovered. A new LLDP frame is received and carries device information
new to the local device.
•
The LLDP operating mode of the LLDP agent changes from Disable or Rx to TxRx or Tx.
With this mechanism, the specified number of LLDP frames are sent successively at a configurable
fast transmission interval to help LLDP neighbors discover the local device as soon as possible.
Then, the normal LLDP frame transmission interval resumes.
Receiving LLDP frames
An LLDP agent operating in TxRx mode or Rx mode confirms the validity of TLVs carried in every
received LLDP frame. If the TLVs are valid, the LLDP agent saves the information and starts an
aging timer. When the TTL value in the Time To Live TLV carried in the LLDP frame becomes zero,
the information ages out immediately.